This invention relates to a method for fabricating a fluorescent lamp, and more particularly to improvements in a mount sealing process for a fluorescent lamp.
In general, a fluorescent lamp is finished up via a process for spreading a phosphor on the inner surface of a glass tube, a process for baking the phosphor, a process for sealing each end part of the glass tube by the use of a mount, a process for exhausting the air from the glass tube, a base attaching process, and an aging process.
In the sealing process among these fabricating processes, each end of the glass tube is melted and sealed with the mount having a filament. A typical prior-art example of such sealing process will be described with reference to FIGS. 1A, 1B and 1C.
(a): First, a straight glass tube 3 is held vertical, and a mount pin 1 carrying a mount 2 is inserted into the glass tube 3. At this time, the flared edge 5 of the mount 2 is located at that position inside the glass tube 3 which is considerably higher than the extremity 7 of the glass tube 3. Whilst rotating the glass tube 3 round its axis with the mount and the glass tube kept in such positional relationship, a burner (not shown) is applied to a position of arrows A and A corresponding substantially to the flared edge 5 of the mount 2 (FIG. 1A).
(b): Then, the part of the glass tube 3 heated by the burner softens and thins to melt and adhere to the flared edge 5 of the mount 2. A cullet 4 which is the lower end part of the glass tube 3 moves down owing to its own weight (FIG. 1B).
(c): By further heating the vicinity B of the melted part of the glass tube 3 as indicated by arrows, the cullet 4 separates, and the sealing of the tube end 6 is completed (FIG. 1C).
The sealing process called the "drop sealing" as illustrated in FIGS. 1A, 1B and 1C has many problems. For example, the cullet 4 in the glass tube 3 becomes wasteful in production, with the result that the material cost becomes high. Moreover, an equipment for the abandonment disposal of the cullet 4 needs to be arranged in production installations.
Another typical prior-art example of the sealing process will now be explained with reference to FIG. 2.
In the case of the figure, the end part 8 of a glass tube 3 is formed into a neck shape and is located in proximity to the flared edge 5 of a mount 2 carried on a mount pin 1. Whilst heating the connected parts A by means of a burner (not shown), they are melted to seal the tube end.
The sealing process called the "butt sealing" as illustrated in FIG. 2 has many problems, too. For example, the end part 8 of the glass tube 3 needs to be formed into the neck shape in advance, so that the price of the glass tube 3 rises. Especially in case where the outside diameter of the glass tube 3 is small, the formation of the neck shape is not easy.